It is proposed to construct glass microelectrodes sensitive to sodium for the purpose of measuring intracellular sodium activity in isolated segments of Amphium small intestine. Simultaneous measurement of the accumulation of galactose by the intestinal absorptive cell will allow assessment of the role of the sodium gradient in the active transport of sugar across the mucosal membrane. In addition the response of the mucosal membrane potential and the transmural potential to the presence of actively transported sugars at various concentrations of extracellular sodium will be investigated. The role of extracellular shunts in the electrical response will be evaluated from the changes in the individual (mucosal and serosal) membrane potentials on addition of sugar.